1. Field of the Invention
The present invention is directed to lasers, and, more particularly, to a technique for generating a combined laser beam.
2. Description of the Related Art
Despite a great deal of investment, attempts to develop monolithic, very high power lasers have met with only very limited success. This is generally because the technology does not scale well with the output power produced. Thermal issues tend to present the greatest challenge and therefore generally are the limiting factors. For example, higher power lasers generate larger amounts of waste heat than become increasingly difficult to dispose of as the power scales upward. But other issues become problematical as well. Non-linear effects begin to predominate, and it becomes more difficult to input the prime power to the laser. Pulsed and continuous wave laser systems suffer from similar problems.
Alternative approaches attempting to overcome these problems include coherent beam combining, wavelength division multiplexing, and geometric overlap at a point. Coherent beam combining has been effective in producing a single, diffraction limited coherent beam. However, this approach places extremely stringent requirements on the laser system and fill factor is often a problem. Open results have proven the principle, but has failed to establish the utility. Wavelength division multiplexing has a long history in the telecommunications industry, which uses low power. But, it requires tunable lasers and wavelength separation requirements limit the number of lasers. Furthermore, the beam combiner is a high loss component and is delicate (i.e., fragile, or not rugged). Geometric overlap techniques have been demonstrated to produce very high powers and are used in, for example, fusion experiments. However, the resultant beams are not suitable for directing energy at range.
Thus, in general, these alternative approaches have not produced high power laser signals at range. They generally impose stringent requirement on beam properties and achieve only modestly higher powers than the low power lasers they employ. In fact, they typically do not generate powers much higher than that which can be obtained from a single optimized laser. These inadequacies are compounded in applications at long range, where the combined beam should look and act like a single, diffraction limited beam to be operationally effective. Simple, effective, long range high power laser systems still have yet to be introduced to the art.
The present invention is directed to resolving, or at least reducing, one or all of the problems mentioned above.